TY - JOUR
T1 - Investigation of thermal decomposition of nitrobenzene: An energetic material
AU - Liu, Dapeng
AU - Farooq, Aamir
N1 - KAUST Repository Item: Exported on 2023-06-07
Acknowledgements: Research reported in this publication was funded by the Office of Sponsored Research at King Abdullah University of Science and Technology (KAUST).
PY - 2023/5/26
Y1 - 2023/5/26
N2 - Oxidation and pyrolysis mechanisms of energetic materials shape their macro properties such as autoignition and detonation. The high reaction-enthalpy, microsecond order reaction time, and toxicity necessitate investigation of their detailed chemical kinetics. A shock tube combined with laser absorption diagnostic provides time-resolved, high-sensitivity, and homogeneous environment to study thermal degradation of energetic and hazardous materials. In this work, we investigated the thermal fragmentation of nitrobenzene (C6H5NO2), a prototypical energetic material and nitro-aromatic representative, behind reflected shock waves. We studied its pyrolysis and decomposition branching channels over temperatures of 1155–1434 K and pressures of 0.82–1.78 bar. Channel-specific branching ratio was determined by employing a two-color laser absorption diagnostic. Two decomposition pathways are found to be significant under our experimental conditions. The first channel (k1) produces phenyl radical (C6H5) and NO2 while the second channel (k2) generates phenoxy radical (C6H5O) and NO. We monitored the reaction progress by tracing channel-specific products, i.e., phenyl radical (C6H5) and NO, using ultraviolet–visible (UV–vis) and infrared (IR) absorption diagnostics. UV–vis light at 445 nm for phenyl radical detection came from the frequency doubling of 890 nm light, generated by a titanium–sapphire laser, which was pumped by a green (532 nm) Nd:YAG laser. IR light at 5.517 μm for NO detection was generated by an external-cavity quantum cascade laser. We extracted the rate coefficients of the two decomposition channels and fitted them in Arrhenius form (units of s−1): [Formula Presented] [Formula Presented] Rate coefficients of both channels show positive temperature dependence while we did not observe discernible pressure dependence over 0.82–1.78 bar. Our measurements agree with a previous theoretical work qualitatively that, under these high-temperature conditions, the decomposition channel producing phenyl radicals and NO2 (k1) prevails over the NO-producing channel. Quantitatively, however, the theoretical work overestimates the importance of k1 channel, particularly at low temperatures. Our rate of production analysis shows that most of the phenyl radicals are consumed through their self-recombination while N atoms are mainly converted to NO2. This work benefits high-fidelity chemical modeling of the relevant safety and ignition aspects of nitrogen-containing energetic/hazardous materials.
AB - Oxidation and pyrolysis mechanisms of energetic materials shape their macro properties such as autoignition and detonation. The high reaction-enthalpy, microsecond order reaction time, and toxicity necessitate investigation of their detailed chemical kinetics. A shock tube combined with laser absorption diagnostic provides time-resolved, high-sensitivity, and homogeneous environment to study thermal degradation of energetic and hazardous materials. In this work, we investigated the thermal fragmentation of nitrobenzene (C6H5NO2), a prototypical energetic material and nitro-aromatic representative, behind reflected shock waves. We studied its pyrolysis and decomposition branching channels over temperatures of 1155–1434 K and pressures of 0.82–1.78 bar. Channel-specific branching ratio was determined by employing a two-color laser absorption diagnostic. Two decomposition pathways are found to be significant under our experimental conditions. The first channel (k1) produces phenyl radical (C6H5) and NO2 while the second channel (k2) generates phenoxy radical (C6H5O) and NO. We monitored the reaction progress by tracing channel-specific products, i.e., phenyl radical (C6H5) and NO, using ultraviolet–visible (UV–vis) and infrared (IR) absorption diagnostics. UV–vis light at 445 nm for phenyl radical detection came from the frequency doubling of 890 nm light, generated by a titanium–sapphire laser, which was pumped by a green (532 nm) Nd:YAG laser. IR light at 5.517 μm for NO detection was generated by an external-cavity quantum cascade laser. We extracted the rate coefficients of the two decomposition channels and fitted them in Arrhenius form (units of s−1): [Formula Presented] [Formula Presented] Rate coefficients of both channels show positive temperature dependence while we did not observe discernible pressure dependence over 0.82–1.78 bar. Our measurements agree with a previous theoretical work qualitatively that, under these high-temperature conditions, the decomposition channel producing phenyl radicals and NO2 (k1) prevails over the NO-producing channel. Quantitatively, however, the theoretical work overestimates the importance of k1 channel, particularly at low temperatures. Our rate of production analysis shows that most of the phenyl radicals are consumed through their self-recombination while N atoms are mainly converted to NO2. This work benefits high-fidelity chemical modeling of the relevant safety and ignition aspects of nitrogen-containing energetic/hazardous materials.
UR - http://hdl.handle.net/10754/692399
UR - https://linkinghub.elsevier.com/retrieve/pii/S0010218023002286
UR - http://www.scopus.com/inward/record.url?scp=85160535198&partnerID=8YFLogxK
U2 - 10.1016/j.combustflame.2023.112847
DO - 10.1016/j.combustflame.2023.112847
M3 - Article
SN - 1556-2921
VL - 254
SP - 112847
JO - Combustion and Flame
JF - Combustion and Flame
ER -